Add existing HPKE project files

crypto/ecdh/interfaces.go

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+// Package ecdh defines an additional interface that will be added to the
+// crypto/ecdh package in Go 1.26+.
+package ecdh
+
+import "crypto/ecdh"
+
+// KeyExchanger is an interface for an opaque private key that can be used for
+// key exchange operations. For example, an ECDH key kept in a hardware module.
+//
+// It is implemented by [ecdh.PrivateKey].
+type KeyExchanger interface {
+	PublicKey() *ecdh.PublicKey
+	Curve() ecdh.Curve
+	ECDH(*ecdh.PublicKey) ([]byte, error)
+}

crypto/ecdh/stubs.go

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+package ecdh
+
+import "crypto/ecdh"
+
+// This file contains stubs to allow importing only this package instead of
+// crypto/ecdh, to minimize the diff.
+
+type Curve = ecdh.Curve
+type PrivateKey = ecdh.PrivateKey
+type PublicKey = ecdh.PublicKey
+
+func X25519() Curve { return ecdh.X25519() }
+func P256() Curve   { return ecdh.P256() }
+func P384() Curve   { return ecdh.P384() }
+func P521() Curve   { return ecdh.P521() }

crypto/interfaces.go

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+// Package crypto defines additional interfaces that will be added to the
+// crypto package in Go 1.26+.
+package crypto
+
+import (
+	"crypto/ecdh"
+	"crypto/mlkem"
+)
+
+// KeyExchanger is an interface for an opaque private key that can be used for
+// key exchange operations. For example, an ECDH key kept in a hardware module.
+//
+// It is implemented by [ecdh.PrivateKey].
+type KeyExchanger interface {
+	PublicKey() *ecdh.PublicKey
+	Curve() ecdh.Curve
+	ECDH(*ecdh.PublicKey) ([]byte, error)
+}
+
+// Encapsulator is an interface for a public KEM key that can be used for
+// encapsulation operations.
+//
+// It is implemented, for example, by [crypto/mlkem.EncapsulationKey768].
+type Encapsulator interface {
+	Bytes() []byte
+	Encapsulate() (sharedKey, ciphertext []byte)
+}
+
+// Decapsulator is an interface for an opaque private KEM key that can be used for
+// decapsulation operations. For example, an ML-KEM key kept in a hardware module.
+//
+// It will be implemented by [crypto/mlkem.DecapsulationKey768] in Go 1.26+.
+// In the meantime, use [DecapsulatorFromDecapsulationKey768] and
+// [DecapsulatorFromDecapsulationKey1024].
+type Decapsulator interface {
+	Encapsulator() Encapsulator
+	Decapsulate(ciphertext []byte) (sharedKey []byte, err error)
+}
+
+// DecapsulatorFromDecapsulationKey768 wraps an ML-KEM-768 decapsulation key
+// into a [Decapsulator], until Go 1.26+ where [crypto/mlkem.DecapsulationKey768]
+// implements it natively.
+func DecapsulatorFromDecapsulationKey768(dk *mlkem.DecapsulationKey768) Decapsulator {
+	return &mlkem768Decapsulator{dk}
+}
+
+type mlkem768Decapsulator struct {
+	*mlkem.DecapsulationKey768
+}
+
+func (d *mlkem768Decapsulator) Encapsulator() Encapsulator {
+	return d.EncapsulationKey()
+}
+
+// DecapsulatorFromDecapsulationKey1024 wraps an ML-KEM-1024 decapsulation key
+// into a [Decapsulator], until Go 1.26+ where [crypto/mlkem.DecapsulationKey1024]
+// implements it natively.
+func DecapsulatorFromDecapsulationKey1024(dk *mlkem.DecapsulationKey1024) Decapsulator {
+	return &mlkem1024Decapsulator{dk}
+}
+
+type mlkem1024Decapsulator struct {
+	*mlkem.DecapsulationKey1024
+}
+
+func (d *mlkem1024Decapsulator) Encapsulator() Encapsulator {
+	return d.EncapsulationKey()
+}